NASHVILLE - Tennessee Attorney General Robert Cooper says a so-called "ag gag" bill passed by state lawmakers is "constitutionally suspect" under the U.S. Constitution's First Amendment.

The 10-page legal opinion, released Thursday, comes as Gov. Bill Haslam continues to wrestle over whether he will sign the bill, veto it or allow it to become law without his signature.

"The governor is reviewing the opinion," Haslam spokesman David Smith said.

The bill requires anyone who intentionally makes a picture or video documenting livestock abuse provide copies to "law enforcement" within 48 hours. Failure to do so would be a misdemeanor with a $500 fine for anyone found guilty.

Haslam faces a deadline Wednesday. Meanwhile, about 15,000 people have bombarded Haslam's office with email and telephone calls, the vast majority urging the governor to veto it.

Celebrities including country music superstar Carrie Underwood have urged him to veto it. Priscilla Presley joined in Thursday.

In the opinion, requested by Rep. Mike Stewart, D-Nashville, Cooper said House Bill 1191 is constitutionally suspect on three grounds.

The first is it is "underinclusive" or discriminatory in who is covered. Secondly, the requirement to provide recordings of livestock cruelty "could be an impermissible prior restraint."

Finally, the opinion says, the reporting requirement "could be found to constitute an unconstitutional burden on news gathering."

"In addition, HB1191 could be held to violate a person's Fifth Amendment right against self-incrimination," the opinion says.

The Humane Society of the United States contends the bill is a thinly veiled effort to block undercover investigations the group conducts into livestock cruelty, including a 2012 long-term investigation the group conducted of the Tennessee walking horse industry.

That resulted in a guilty plea last year in U.S. District Court in Chattanooga from a West Tennessee trainer caught on video beating and using chemicals to burn horses' legs to produce a high gait.

The bill's sponsors, however, argue the would-be law is aimed at providing relief to animals suffering torture as quickly as possible. They and other critics contend video can be edited selectively to distort activity.

The Tennessee Farm Bureau backed the bill. Critics say it was inspired by a model bill promoted by the American Legislative Exchange Council, a conservative group comprised of conservative lawmakers and companies.

Senate Speaker Ron Ramsey, R-Blountville, supported the bill and said he hopes Haslam signs it. While the bill passed the Senate overwhelmingly, it scraped through the House with only the legally required 50 votes required to pass it. House Speaker Beth Harwell, R-Nashville, opposed it.

Earlier this week, Haslam told reporters that "at the end of the day, it [decision] should be about is the bill constitutional. Does it encourage the healthy treatment of animals, and is it good public policy that's well-written for the state. That's what we're going to make our decision based on."

Wayne Pacelle, president and CEO of the Humane Society of the United States, later released a statement, saying, "any bill that tries to punish those who expose cruelty, rather than those who perpetrate it, is wrong-headed and reckless. Now we know it's constitutionally deficient, too."

Noting Haslam now has a "superabundance of legal and citizen input that should prompt him to veto this overreaching, awful measure."